1. Field of the Invention
The present invention relates to a capacity type semiconductor dynamic quantity sensor which provides the displacement of a movable portion in response to a dynamic quantity acting thereon as a sensor output and a method for manufacturing the same.
2. Description of the Related Art
For example, a capacity type semiconductor acceleration sensor has a configuration in which a beam structure is provided as a movable portion displaced in response to acceleration acting thereon. The displacement of the beam structure is output as a change in the capacity of a capacitor formed between a movable electrode provided integrally with the beam structure and a fixed electrode provided on a substrate. As disclosed in Japanese Patent Application Laid-Open No. 6-349806 and etc., such a semiconductor acceleration sensor has been manufactured using a method including the steps of providing a semiconductor substrate having an SOI structure by forming a second semiconductor layer on a first semiconductor layer (support substrate) with an insulation layer interposed therebetween, patterning the first semiconductor layer into a predetermined configuration in accordance with the configurations of the beam structure, fixed electrode and the like, and etching the insulation layer as a sacrificial layer. The beam structure having the movable electrode and the fixed electrode is eventually formed on a semiconductor substrate.
The above-described manufacturing method must inevitably include the step of etching the sacrificial layer using an etchant. At the step of etching the sacrificial layer, the surface tension of the etchant frequently causes the so-called sticking phenomenon that is sticking of the beam structure (especially the movable electrode) to other regions (particularly, the fixed electrode). Such a phenomenon leads to a failure in that the detection of any change in the capacity between the movable and fixed electrodes is disabled. This has resulted in a problem with the manufacturing method in the prior art in that it inevitably results in a reduction of yield.
It has been also revealed in that a conventional capacity type semiconductor dynamic quantity sensor has a problem as described below when the second semiconductor layer having the movable and fixed electrodes formed therein and the first semiconductor layer supporting the same (support substrate) have relatively high specific resistances.
Specifically, in general, a capacity type semiconductor dynamic quantity sensor utilizes a carrier wave signal having a relatively high frequency to output a change in the capacity thereof. In this case, when a voltage in accordance with the carrier wave signal is applied between the movable and fixed electrodes forming a capacitor, charge is generated at a side of the movable electrode which corresponds to the product of the capacity of the capacitor and a potential difference between the fixed electrode and itself. Any change in the capacity of the capacitor is output using the movement of the charge.
The charge movement thus caused involves a path for applying the voltage to the movable and fixed electrodes and a time constant that depends on the resistance and capacity of a path for outputting the charge. However, since such paths include resistive elements (including the movable and fixed electrodes themselves) formed by the second semiconductor layer and parasitic resistive elements formed on the first semiconductor layer through the insulation layer, the time constant is larger when the first and second semiconductor layers have relatively high specific values of resistance. Such a large time constant suppresses the rate of the charge movement and delays the rise of the carrier wave signal. Therefore, the detection of dynamic quantities utilizing the capacity of the capacitor provides results deviated from values which should normally be obtained, resulting in deterioration of dynamic quantity detection characteristics.